internal/util/projutil: add function to exit if not a Go project

commands/operator-sdk/{add,generate}: exit if not a Go project for
'add {api,controller}', 'generate k8s' sub-commands

Author: estroz

Diff for: commands/operator-sdk/cmd/add/api.go

@@ -63,6 +63,9 @@ Example:
 }
 
 func apiRun(cmd *cobra.Command, args []string) {
+	// Only Go projects can add apis.
+	projutil.MustGoProject("add api")
+
 	// Create and validate new resource
 	projutil.MustInProjectRoot()
 	r, err := scaffold.NewResource(apiVersion, kind)

Diff for: commands/operator-sdk/cmd/add/controller.go

@@ -57,6 +57,9 @@ Example:
 }
 
 func controllerRun(cmd *cobra.Command, args []string) {
+	// Only Go projects can add controllers.
+	projutil.MustGoProject("add controller")
+
 	projutil.MustInProjectRoot()
 	// Create and validate new resource
 	r, err := scaffold.NewResource(apiVersion, kind)

Diff for: commands/operator-sdk/cmd/generate/k8s.go

@@ -48,6 +48,9 @@ func k8sFunc(cmd *cobra.Command, args []string) {
 
 // K8sCodegen performs deepcopy code-generation for all custom resources under pkg/apis
 func K8sCodegen() {
+	// Only Go projects can generate k8s deepcopy code.
+	projutil.MustGoProject("generate k8s")
+
 	projutil.MustInProjectRoot()
 	repoPkg := projutil.CheckAndGetCurrPkg()
 	outputPkg := filepath.Join(repoPkg, "pkg/generated")

Diff for: internal/util/projutil/project_util.go

@@ -52,6 +52,13 @@ func MustInProjectRoot() {
 	}
 }
 
+// MustGoProject checks if the current project is a Go project, and exits if not.
+func MustGoProject(cmd string) {
+	if GetOperatorType() != OperatorTypeGo {
+		log.Fatalf("'operator-sdk %s' can only be run for Go projects", cmd)
+	}
+}
+
 func MustGetwd() string {
 	wd, err := os.Getwd()
 	if err != nil {